1. Field of the Invention
The present invention relates to a rubber composition for tires, hoses, conveyor belts and the like and which has an improved reinforcing property, particularly improved heat generation and processability.
2. Related Art Statement
Carbon blacks such as ISAF or the like, possessing highly reinforcing ability have formerly been used for rubber compositions in treads of tires for trucks and buses, and the like in which considerably high wear resistance is required. In recent years, as the demand for economy has become greater in the market, it is important to attain higher wear resistance from the standpoint of the determination of product value.
In order to improve wear resistance, the compounding recipe is varied, for instance, the compounding ratio of carbon black is increased or the amount of a softener such as a process oil is decreased, or, alternatively, SAF grade carbon black having an excellent reinforcing ability is used instead of ISAF grade carbon black.
However, if the compounding ratio of carbon black is increased, the wear resistance is indeed improved within a certain range of the compounding ratio. But, as the compounding ratio increases, demerits become greater. For example, with an increase in the compounding ratio, the effect obtained gradually decreases, and the wear resistance of the rubber composition lowers.
On the other hand, if the ratio of the softening agent such as process oil is decreased, tacking of the kneaded rubber composition becomes poorer, although the wear resistance is improved. In addition, the viscosity of the rubber increases. Thereby, operability is deteriorated to a large extent.
Further, when the SAF grade carbon black is used, operability becomes poorer due to increased viscosity, although wear resistance is improved.
Under the circumstances, although various investigations have been made with respect to extension of the rubber-kneading time period and production techniques, sufficient effects could not be obtained prior to the present invention.